Grass mowing machines known as zero turning radius (“ZTR”) mowers have at least one independently powered drive wheel on each side of a frame. Many ZTR mowers have a twin stick control system. A pair of control levers or sticks may be provided side-by-side, with each lever or stick controlling one of the drive wheels. When both levers or sticks are advanced together forwardly out of their neutral position, both drive wheels rotate forwardly to cause the mower to move forward. A ZTR mower may be steered by advancing one lever or stick more than the other.
Typically, each control lever or stick on a ZTR mower may be linked to a pump arm of one of two separate hydraulic pumps, or of a dual hydraulic pump; i.e., a separate pump for each wheel. The lever or stick may be used to move a pump swash plate through a direct linkage.
The control levers or sticks on a ZTR mower may be mounted on the vehicle frame so that each has a first pivot axis allowing the lever or stick in the operating position to pivot forwardly in an arc to turn the wheel in forward, or pivot rearwardly to turn the wheel in reverse. Additionally, the operator can pivot each lever or stick to a neutral operating position, and then pivot each lever or stick outwardly in an arc to a non-operating or park position.
Some ZTR mowers have start circuits that require the control levers or sticks to be pivoted outward, and also require engagement of a parking brake. Other ZTR mowers activate the parking brake on each drive wheel by moving the steering levers outward. For example, U.S. Pat. No. 6,434,917 relates to a ZTR mower with combined steering and brake levers in which the levers are each connected through a first series of linkages to the hydraulic pump control, and through second linkages which lock the brake on each wheel. Before the engine can be started, a micro switch must be closed and the parking brakes must be set by pivoting both levers out.
Additionally, U.S. Pat. No. 6,739,116 relates to a powered actuator system for a ZTR mower parking brake system. The powered actuator system automatically engages the parking brakes when the operator places the control sticks into their laterally pivoted, outboard positions. The powered actuator system includes electrical sensors or switches that detect if the control sticks are placed in their outboard positions. The electrical sensors or switches are connected by a circuit having a solenoid that is energized or deenergized to engage or disengage the parking brake system.
However, due to wear, slop in the system, and contamination, electrical sensors, switches or electromechanical devices used in return to neutral control mechanisms sometimes have failed to recognize if the control levers or sticks are in their outboard positions. As a result, the ZTR mower will not start or the parking brake cannot be used. Additionally, some ZTR mower operators may wish to apply the parking brake, or start the engine, without pivoting both control levers or sticks to their outboard positions.
To overcome these problems, a return to neutral control mechanism for a ZTR mower is needed that is not subject to wear, slop in the system, or contamination, and that will help ensure the mower can be started if the parking brake is engaged. A return to neutral control mechanism for a ZTR mower is needed that will eliminate electrical switches or sensors that apply the parking brakes if the control levers or sticks are at the neutral position. A return to neutral control mechanism for a ZTR mower is needed that allows the parking brake to be locked if the control levers or sticks are at their outboard or inboard positions.